Terminal device, base station device, retransmission method, and resource allocation method

ABSTRACT

The present invention provides a terminal device that allows constraints on user allocation to be prevented and spread codes to be allocated in a scheduler when non-adaptive HARQ is employed using a PHICH. A codeword generator ( 103 ) generates code words (CW) by encoding data, a layer mapping unit ( 108 ) places each CW in one or a plurality of layers, a DMRS generator ( 110 ) generates a reference signal for each layer in which a CW is placed by using any resource among a plurality of resources defined by a mutually orthogonal plurality of OCCs, and an ACK/NACK demodulator ( 102 ) receives a response signal indicating a retransmission request. When a response signal requesting retransmission of only a CW placed in a plurality of layers is received, the DMRS generator ( 110 ) uses each resource having the same OCC among the plurality of resources for the reference signals generated in the corresponding layers.

TECHNICAL FIELD

The present invention relates to a terminal apparatus, a base stationapparatus, a retransmission method and a resource allocating method.

BACKGROUND ART

In recent years, attempts have been made to improve throughput byproviding a plurality of antennas on both a base station apparatus(referred to simply as a base station hereinafter) and a terminalapparatus (referred to simply as a terminal hereinafter) to introducethe MIMO (multiple-input multiple-output) communication technology onuplink. In this MIMO communication technology, a study is made on datatransmission using precoding control in a terminal. In the precodingcontrol, the base station estimates a channel condition between the basestation and the terminal, from a receiving condition of a referencesignal (Sounding Reference Signal: SRS) independently transmitted fromeach antenna of the terminal, selects a precoder which is optimal forthe estimated channel condition and applies the precoder to datatransmission.

Particularly, precoding control based on a transmission rank is appliedto LTE-Advanced (Long Term Evolution-Advanced: hereinafter, referred toas a LTE-A). Specifically, the base station selects the most suitablerank and precoder for the channel matrix formed by the values ofobserved SRSs transmitted from the terminal. Herein, a rank refers tothe number of space multiplexing (the number of layers) in spacedivision multiplexing (SDM) and is the number of independent datatransmitted at the same time. To be more specific, code books havingdifferent sizes are employed for respective ranks. The base stationreceives a reference signal transmitted from the terminal, estimates achannel matrix from the received signal, and selects a rank and aprecoder which is optimal for the estimated channel matrix.

In a communication path such as mobile communication, having arelatively large channel variation, a hybrid automatic repeat request(HARQ) is applied for an error controlling technique. HARQ is atechnique whereby the transmitting side retransmits data, and thereceiving side combines the received data and the retransmitted data toimprove error correction performance and achieve high qualitytransmission. As a HARQ method, adaptive HARQ and non-adaptive HARQ areunder study. Adaptive HARQ is a method for allocating retransmitted datato any resource. On the other hand, non-adaptive HARQ is a method forallocating retransmitted data to predetermined resources. In an uplinkof LTE, the non-adaptive HARQ scheme is employed among HARQ schemes.

A non-adaptive HARQ scheme will be described with reference to FIG. 1.In non-adaptive HARQ, the base station determines resources forallocating data in the first data allocation. The base station thenreports transmission parameters to a terminal through a downlink controlchannel (PDCCH: Physical Downlink Control Channel). The transmissionparameters include information such as allocated frequency resourcesindicating information on resource allocation, a transmission ranknumber, a precoder, and a modulation scheme/a coding rate. The terminalacquires the transmission parameters transmitted through the PDCCH andtransmits first data, using a predetermined resource in accordance withthe aforementioned resource allocation information.

The base station receives the first data and reports, to the terminal, aNACK corresponding to data which could not be demodulated in the firstdata, through a HARQ reporting channel (PHICH: Physical. Hybrid-ARQIndicator Channel). The terminal receives the NACK and controlsretransmission by using the transmission parameters reported through thePDCCH, the parameters including information resource allocation and thelike. Specifically, the terminal generates and transmits retransmissiondata, using an allocation frequency resource, a precoder, a modulationscheme, and the like, which are the same as those in the firsttransmission. The terminal changes an RV (Redundancy Version) parameterdepending on the number of retransmission requests. The RV parameterrepresents a reading position in a memory (referred to as a circularbuffer) for storing Turbo-coded data. For example, when the memory isequally divided into approximately four regions and tops of the areasare assigned zero, one, two, and three respectively, the terminalchanges an RV parameter (a reading position) in order of zero, two, one,three, and zero depending on the number of retransmission requests.

Non-adaptive HARQ is often used together with Synchronous HARQ employingthe constant transmission interval. In LTE, retransmission data isretransmitted eight subframes after the report of the NACK.

Non-adaptive HARQ is performed on a per predetermined control unitbasis, the control unit is referred to as a code word (CW). The CW is acontrol unit to which the same modulation scheme and coding rate areapplied. As with the CW processed in a physical layer dealing withmodulation and coding, the control unit may be referred to as atransport block (TB) since the control unit is processed in a MAC layerdealing with HARQ, and the CW may be distinguished from the TB. Thepresent embodiment however employs uniform notation “CW” without adistinction therebetween hereafter.

In LTE, the transmission of one CW is generally applied to rank 1 (intransmission in a single rank) in the first transmission, and thetransmission of two CWs is applied to ranks 2, 3, and 4 (in transmissionin multiple ranks) in the first transmission. In the transmission inmultiple ranks, CW0 is allocated to Layer 0 and CW1 is allocated toLayer 1 in rank 2. In rank 3, CW0 is allocated to Layer 0, and CW1 isallocated to Layer 1 and Layer 2. In rank 4, CW0 is allocated to Layer 0and Layer 1, and CW1 is allocated to Layer 2 and Layer 3.

When retransmitting only CWs allocated to a plurality of layers, theterminal transmits one CW at a time in rank 2. To be more specific, whenretransmitting CW1 in rank 3 and CW0 or CW1 in rank 4, the terminaltransmits these CWs as one CW in rank 2.

Since the base station includes a larger number of antennas compared tothe terminal, the base station is flexibly installed relatively. Forthis reason, a so-called multiuser MIMO, which assigns the same resourceto a plurality of terminals, can be applied through an adequate processon a received signal in the base station. An example case will bedescribed where the same resource is allocated to two terminals throughthe terminal having one transmitting antenna and the base station havingtwo receiving antennas. This case can be equivalently treated as a MIMOchannel with two transmitting antennas and two receiving antennas, andthe base station can process a received signal. To be more specific, thebase station performs a general MIMO received-signal process such asspatial filtering, canceller, and maximum likelihood estimation, therebydetecting respective signals transmitted from a plurality of terminals.With multiuser MIMO, the base station estimates interference valuesbetween terminals based on the channel condition between the basestation and each terminal, and sets transmission parameters for therespective terminals by considering interference values, in order tomore stably operate a communication system.

As described above, a MIMO operation for a single terminal (a singleuser) provided with a plurality of antennas is sometimes referred to asa single-user MIMO to distinguish it from the multiuser MIMO. Anoperation to allocate a plurality of terminals, each of which is capableof a single-user MIMO operation and has more than one transmissionantennas provided thereon, to the same resource is also referred to as amultiuser MIMO.

The terminal transmits not only the SRS described above but also ademodulation reference signal (Demodulation RS or DMRS) to the basestation, and the base station uses the received DMRS for demodulatingdata. In LTE-A, the DMRS is transmitted for each layer. The terminaltransmits the DMRS using the same precoding vector as that of the signaltransmitted for each layer. In order for a plurality of terminals totransmit the DMRSs for a plurality of layers in the same frequencyresource, some multiplexing process is needed. In LTE-A, as a process ofmultiplexing the DMRSs, multiplexing using an orthogonal cover code(OCC) is used in addition to multiplexing using a cyclic shift sequenceused in LTE to multiplex a plurality of terminals.

The cyclic shift sequence is generated by cyclic shift of apredetermined one of CAZAC (constant amplitude zero auto-correlation)sequences having good auto-correlation characteristics and a constantamplitude. For example, twelve cyclic shift sequences each of whichhaving a starting point at one of twelve points that equally divide aCAZAC sequence along the code length are used. In the following, thestarting point will be expressed as n_(CS).

As for the OCC, spreading codes having a sequence length of 2 are formedusing a DMRS, which includes two symbols per sub-frame, taking intoconsideration the transmission format of the uplink data. To be morespecific, in LTE-A, as OCCs, two spreading codes having a sequencelength of 2, {+1, +1} and {+1, −1}, are formed. In the following, aspreading code according to the OCC will be expressed as n_(OCC). Forexample, the two spreading codes {+1, +1} and {+1, −1} are expressed asn_(OCC)=0 and 1, respectively.

Further, n_(CS) and n_(OCC) are included in transmission parametersreported from the base station to the terminal through the PDCCH. Aspecific method of reporting the transmission parameters includingn_(CS) and n_(OCC), in particular, a specific reporting method using thesingle-user MIMO, will be described later.

Next, interference between DMRSs multiplexed in the same frequencyresource will be described. FIG. 2 is a schematic diagram showinginterference between DMRSs to which n_(CS)=6 and n_(OCC)=0 areallocated. The interference between the DMRSs formed by the cyclic shiftsequence and the OCC described above is characterized in that the DMRSshaving the same value of n_(OCC) and adjacent values of n_(CS) interferewith each other. For example, reference signals having the same value ofn_(OCC) and adjacent values of n_(CS) that differ from each other by upto 3 or so (indicated by the arrows in FIG. 2) (that is, referencesignals whose n_(OCC) is 0 and whose n_(CS) falls within a range of 3 to5 or a range of 7 to 9 in FIG. 2) interfere with each other. Therefore,as for n_(CS), in order for reference signals to be allocatable at thesame time, the values of n_(CS) of the reference signals preferablydiffer by 6 or so.

As for n_(OCC), on the other hand, if reference signals to be allocated(to be multiplexed) at the same time have the same code length, that is,the same bandwidth allocated thereto, the reference signals are expectedto be orthogonal to each other if they have different values of n_(OCC).The degree of the orthogonality (referred to simply as orthogonality)depends on the fading correlation between the two symbols in onesub-frame to which the reference signals (DMRSs) are allocated. Forexample, in a low-speed moving environment, which is a primaryapplication of MIMO, high orthogonality is expected to be assured.

Next, a method of reporting a spreading code of a DMRS in thesingle-user MIMO will be described. According to a method of reporting aspreading code of a DMRS in LTE, the base station sets arbitraryspreading codes using a parameter n_(DMRS) ⁽¹⁾ set for each user in ahigher layer assuming a relatively long period and a parameter n_(DMRS)⁽²⁾ that is a transmission parameter reported through the PDCCH and setfor a relevant transmission sub-frame by decision of the scheduler, andindicates the spreading codes to the terminal. The terminal generates aDMRS using a prescribed n_(CS) calculated from the indicated parameter(n_(DMRS) ⁽¹⁾ or n_(DMRS) ⁽²⁾).

In LTE-A, there is proposed a method of expanding the reporting methoddescribed above to the single-user MIMO (see Non-Patent Literature 1,for example). In Non-Patent Literature 1, the starting point of thecyclic shift sequence and the set value of OCC for the k-th layer (k=0to 3) are set as n_(DMRS,k) ⁽²⁾ (corresponding to n_(CS) describedabove) and n_(OCC,k), respectively. In Non-Patent Literature 1,information reported through higher layers or the PDCCH is only the setvalues (n_(DMRS,0) ⁽²⁾ and n_(OCC,0)) for the 0-th layer (k=0, Layer 0),and the set values for the remaining layers (k=1 to 3, Layers 1 to 3)are determined by calculation from the set values for the 0-th layer(k=0, Layer 0). This is an attempt to minimize the overhead involved inreporting of the controlling signal.

To be more specific, Non-Patent Literature 1 discloses that each setvalue is set as follows in order to avoid the interference between thereference signals as far as possible in the single-user MIMO.

Specifically, n_(DMRS,0) ⁽²⁾ is defined as (n_(DMRS,0) ⁽²⁾+Δ_(k)) mod 12

where

in transmission using two layers, Δ_(k)=0 for k=0, and Δ_(k)=6 for k=1,

in transmission using three layers, Δ_(k)=0 for k=0, Δ_(k)=6 for k=1,and Δ_(k)=3 for k=2, or

Δ_(k)=0 for k=0, Δ_(k)=4 for k=1, and Δ_(k)=8 for k=2, and

in transmission using four layers, Δ_(k)=0 for k=0, Δ_(k)=6 for k=1,Δ_(k)=3 for k=2, and Δ_(k)=9 for k=3.

Further, n_(OCC,k) is defined as n_(OCC,0) or (1−n_(OCC,0))

where

n_(OCC,k)=n_(OCC,0) for k=1, and n_(OCC,k)=(1−n_(OCC,0)) for k=2 or 3.

CITATION LIST Non-Patent Literature NPL 1

-   R1-104219, “Way Forward on CS and OCC signalling for UL DMRS”,    Panasonic, Samsung, Motorola, NTT DOCOMO, NEC, Panatech

SUMMARY OF INVENTION Technical Problem

A case where a terminal transmits data using the above-describedconventional method for allocating spreading codes of a reference signal(DMRS), and a base station applies non-adaptive HARQ control using aPHICH will be described. In this case, the PHICH used for instructingdata retransmission cannot carry information on transmission parameters.As a result, the same spreading codes for the reference signal as thoseused in the first transmission are used in retransmission of data, morespecifically, retransmission of a CW in response to a NACK returned fromthe base station.

For example, in the case where the first transmission is transmissionusing three layers (rank 3 transmission) as shown in FIG. 3, thespreading codes (CS (starting point n_(CS,k)) and OCC (code n_(OCC,k)))used for each layer (k=0 to 3) are the following three sets: n_(CS,0)=0and n_(OCC,0)=0, n_(CS,1)=6 and n_(OCC,1)=0; and n_(CS,2)=3 andn_(OCC,2)=1. As shown in FIG. 3, it is assumed that the base stationreports an instruction for retransmission of only CW1 in the PHICH tothe terminal (CW0: ACK, CW1: NACK). Then, the spreading codes used inretransmission of CW1 are the same two sets as those used in the firsttransmission: n_(CS,1)=6 and n_(OCC,1)=0, and n_(CS,2)=3 andn_(OCC,2)=1. The two sets of spreading codes occupy both OCCs(n_(OCC,k)=0 and 1).

As a result, only the resources of spreading codes (referred to as aspreading code resource, hereinafter) in the region enclosed by thedashed line in the right half (in retransmission) of FIG. 3 areavailable for allocation to a new user to be multiplexed in the sameresource. To be more specific, as shown in the right half of FIG. 3, forboth OCCs (n_(OCC,k)=0 and 1), spreading code resources having n_(C)swhose values differ by 6 or so are not available for allocation to a newuser.

Thus, as shown in FIG. 3, when the scheduler at the base station is tomultiplex a new user that performs transmission using two layers as amultiuser MIMO operation (when spreading codes having the same value ofOCC and values of n_(CS) that differ by 6 or so are to be used), thereare no available spreading code resources, and no spreading coderesources can be allocated to the new user.

As described above, when non-adaptive HARQ control is applied using thePHICH, there are restrictions on allocation of spreading codes to a newuser by the scheduler.

An object of the present invention is to provide a terminal apparatus, abase station apparatus, a retransmitting method and a resourceallocating method that allow a scheduler to perform a spreading codeallocating operation by avoiding restrictions on allocation of aspreading code to a new user even in the case where non-adaptive HARQcontrol is applied using a PHICH.

Solution to Problem

A terminal apparatus reflecting an aspect of the present invention has:a code word generating section that generates a code word by encoding adata sequence; a mapping section that allocates each code word to one ora plurality of layers; a reference signal generating section thatgenerates a reference signal for each of the layers to which the codeword is allocated, using any of resources from among a plurality ofresources defined by a plurality of codes orthogonal to each other; anda receiving section that receives a response signal indicating aretransmission request for the code word, and in a case where thereceived response signal is to request for retransmission of only asingle code word allocated to the plurality of layers, the referencesignal generating section uses resources having a same code from amongthe plurality of resources, for the reference signal generated for eachof the plurality of layers.

A base station reflecting an aspect of the present invention has: areceiving section that receives a code word allocated to one or aplurality of layers; a detecting section that detects an error of thereceived code word; a response signal generating section that generatesa response signal indicating a result of error detection of the codeword; and a scheduling section that allocates any of resources fromamong a plurality of resources defined by a plurality of codesorthogonal to each other, to the reference signal to be transmitted fromeach terminal apparatus and to be generated for each of the layers towhich the code word is allocated, and in a case where only the result oferror detection of a single code word allocated to the plurality oflayers shows a NACK, the scheduling section identifies resources usedfor the reference signal for each of the plurality of layers transmittedfrom a terminal apparatus to retransmit the single code word, asresources having a same code from among the plurality of resources, andallocates a resource having a different code than the same code fromamong the plurality of resources, to the reference signal transmittedfrom another terminal apparatus different from the terminal apparatus toperform the retransmission.

A retransmitting method reflecting an aspect of the present inventionincludes: generating a code word by encoding a data sequence; allocatingeach code word to one or a plurality of layers; generating a referencesignal for each of the layers to which the code word is allocated, usingany of resources from among a plurality of resources defined by aplurality of codes orthogonal to each other; and receiving a responsesignal indicating a retransmission request for the code word, and in acase where the received response signal is to request for retransmissionof only a single code word allocated to the plurality of layers,resources having a same code from among the plurality of resources areused for the reference signal generated for each of the plurality oflayers.

A resource allocating method reflecting an aspect of the presentinvention includes: receiving a code word allocated to one or aplurality of layers; detecting an error of the received code word;generating a response signal indicating a result of error detection ofthe code word; and allocating any of resources from among a plurality ofresources defined by a plurality of codes orthogonal to each other, tothe reference signal to be transmitted from each terminal apparatus andto be generated for each of the layers to which the code word isallocated, and in a case where only the result of error detection of asingle code word allocated to the plurality of layers shows a NACK,resources used for the reference signal for each of the plurality oflayers transmitted from a terminal apparatus to retransmit the singlecode word are identified as resources having a same code from among theplurality of resources, and a resource having a different code than thesame code from among the plurality of resources is allocated to thereference signal transmitted from another terminal apparatus differentfrom the terminal apparatus to perform the retransmission.

Advantageous Effects of Invention

According to the present invention, even in the case where non-adaptiveHARQ control is applied using a PHICH, it is possible for a scheduler toperform a spreading code allocating operation by avoiding restrictionson allocation of a spreading code to a new user.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a non-adaptive HARQ scheme;

FIG. 2 is a diagram for illustrating interference between referencesignals (DMRSs);

FIG. 3 illustrates the scheme disclosed in Non-Patent Literature 1;

FIG. 4 is a block diagram showing a configuration of main components ofa transmitting apparatus according to Embodiment 1 of the presentinvention;

FIG. 5 is a block diagram showing a configuration of main components ofa receiving apparatus according to Embodiment 1 of the presentinvention;

FIG. 6 is a diagram for illustrating a spreading code allocating processaccording to Embodiment 1 of the present invention;

FIG. 7 is a block diagram showing a configuration of main components ofa transmitting apparatus according to Embodiment 2 of the presentinvention;

FIG. 8 is a block diagram showing a configuration of main components ofa transmitting apparatus according to Embodiment 3 of the presentinvention;

FIG. 9 is a diagram for illustrating a spreading code setting processaccording to Embodiment 3 of the present invention; and

FIG. 10 is a diagram for illustrating a spreading code allocatingprocess according to Embodiment 3 of the present invention;

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will now be described in detailwith reference to the drawings.

Embodiment 1

FIG. 4 is a block diagram showing a configuration of main components ofa transmitting apparatus according to the present embodiment.Transmitting apparatus 100 in FIG. 4 is applied to, for example, anLTE-A terminal. In order to avoid complicated explanation, FIG. 4 showscomponents associated with transmission of uplink data which is closelyrelated to the present invention and components associated withreception of downlink response signals to that uplink data, and theillustration and explanation of components associated with reception ofdownlink data will be omitted.

PDCCH demodulating section 101 demodulates transmission parameters(parameters associated with data transmission) determined in a basestation, from a PDCCH included in a signal transmitted from the basestation (a receiving apparatus described later). The transmissionparameters include information such as allocated frequency resources(allocated resource blocks (RBs), for example), a transmission ranknumber, a precoder, a modulation scheme, a coding rate, RV parametersused in retransmission, or spreading codes for the reference signal(DMRS) associated with a 0-th layer (k=0, Layer 0) (n_(CS,0) (orn_(DMRS,0) ⁽²⁾) and n_(OCC,0) described above, for example). PDCCHdemodulating section 101 outputs the demodulated transmission parametersto rate matching section 105, modulating section 107, layer mappingsection 108, DMRS generating section 110 and SC-FDMA signal generatingsection 113.

ACK/NACK demodulating section 102 demodulates, for each CW, ACK/NACKinformation indicating the result of error detection of the receivedsignal at the base station, from a PHICH included in the signaltransmitted from the base station (the receiving apparatus describedlater). Then, ACK/NACK demodulating section 102 outputs the demodulatedACK/NACK information to rate matching section 105, layer mapping section108 and DMRS generating section 110.

The number of code word generating sections 103 depends on the number ofcode words (CW), and code word generating section 103 generates a CW byencoding input transmission data (a data sequence). Each code wordgenerating section 103 includes coding section 104, rate matchingsection 105, interleaving/scrambling section 106 and modulating section107.

Coding section 104 receives transmission data, provides CRC (CyclicRedundancy Checking) to the transmission data, encodes the data togenerate coded data, and outputs the generated coded data to ratematching section 105.

Rate matching section 105 includes a buffer and stores the coded data inthe buffer. Rate matching section 105 then performs a rate matchingprocess on the coded data based on the transmission parameters outputtedfrom PDCCH demodulating section 101 to adaptively adjust an M-arymodulation value or a coding rate. Rate matching section 105 thenoutputs the coded data subjected to the rate matching process tointerleaving/scrambling section 106. In retransmission (if the ACK/NACKinformation from ACK/NACK demodulating section 102 shows a NACK), ratematching section 105 reads a predetermined amount of coded datadepending on the M-ary modulation value and the coding rate asretransmission data, from the starting position in the buffer indicatedby the RV parameter outputted from PDCCH demodulating section 101. Ratematching section 105 then outputs the read retransmission data tointerleaving/scrambling section 106.

Interleaving/scrambling section 106 performs an interleaving/scramblingprocess on the coded data received from rate matching section 105 andoutputs the coded data subjected to the interleaving/scrambling processto modulating section 107.

Modulating section 107 performs an M-ary modulation on the coded databased on the transmission parameters received from PDCCH demodulatingsection 101 to generate modulated signals and outputs the modulatedsignals to layer mapping section 108.

Layer mapping section 108 maps, to each layer on a CW basis, themodulated signals received from modulating section 107 in each code wordgenerating section 103 based on the transmission parameters receivedfrom PDCCH demodulating section 101 and the ACK/NACK informationreceived from ACK/NACK demodulating section 102. Herein, layer mappingsection 108 maps (allocates) each CW to one or more layers depending onthe transmission rank number included in the transmission parameters, asdescribed above. Layer mapping section 108 then outputs the mapped CWsto precoding section 109.

Precoding section 109 performs precoding process on the DMRS receivedfrom DMRS generating section 110 or the CWs received from layer mappingsection 108 to apply a weight to each DMRS or CW. Precoding section 109then outputs precoded CWs and DMRS to SC-FDMA (Single Carrier FrequencyDivision Multiple Access) signal generating section 113.

DMRS generating section 110 generates a DMRS for each of the layers,which depends on the transmission rank number, based on the transmissionparameters received from PDCCH demodulating section 101 and the ACK/NACKinformation received from ACK/NACK demodulating section 102. In thepresent embodiment, a plurality of spreading code resources for DMRSsare defined based on cyclic shift sequences that can be separated fromeach other using different amounts of cyclic shift (n_(CS,k)=0 to 11,for example) and OCCs that are orthogonal to each other (n_(OCC,k)=0, 1,for example). DMRS generating section 110 generates a DMRS for eachlayer to which a CW is allocated, using any of the plurality ofspreading code resources for DMRSs.

To be more specific, DMRS generating section 110 calculates, based onthe spreading codes (n_(CS,0) and n_(OCC,0), for example) used in theDMRS associated with the 0-th layer (k=0, Layer 0), included in thetransmission parameters, as described above, the spreading codes used inthe DMRS associated with each of the other layers (k=1, 2 and 3, Layers1, 2 and 3). DMRS generating section 110 outputs the spreading codesgenerated based on the transmission parameters received from PDCCHdemodulating section 101 (that is, the spreading codes used in the DMRSindicated by the base station through the PDCCH) to retransmissionspreading code storage section 111. If the ACK/NACK information receivedfrom ACK/NACK demodulating section 102 shows a NACK (that is, ifretransmission is required), DMRS generating section 110 sets spreadingcodes used in the DMRS in CW retransmission based on the CW associatedwith the NACK and the spreading codes stored in retransmission spreadingcode storage section 111. A DMRS generating process conducted by DMRSgenerating section 110 in retransmission will be described later.

Retransmission spreading code storage section 111 stores the spreadingcodes received from DMRS generating section 110 (that is, the spreadingcode resource used for the DMRS generated for each layer in the firsttransmission and indicated through the PDCCH). Retransmission spreadingcode storage section 111 outputs the spreading codes stored therein toDMRS generating section 110 in response to a request from DMRSgenerating section 110.

SRS (Sounding Reference Signal) generating section 112 generatesreference signal for measuring channel quality (SRS) and outputs thegenerated SRS to SC-FDMA signal generating section 113.

SC-FDMA signal generating section 113 performs SC-FDMA modulation on thereference signal (SRS) received from SRS generating section 112 or theprecoded CW and DMRS to generate an SC-FDMA signal. SC-FDMA signalgenerating section 113 then performs a radio transmitting process (S/P(Serial/Parallel) transform, inverse Fourier transform, upconvert,amplification, and the like) on the generated SC-FDMA signal andtransmits the signal subjected to the radio transmitting process throughtransmitting antennas. In view of the above, the first transmission dataor retransmission data is transmitted to the receiving apparatus.

FIG. 5 is a block diagram showing a configuration of main components ofa receiving apparatus according to the present embodiment. Receivingapparatus 200 in FIG. 5 is applied to, for example, an LTE-A basestation. Note that, to avoid complication of explanation, FIG. 5 showscomponents associated with reception of uplink data which is closelyrelated to the present invention and components associated withtransmission of downlink response signals to that uplink data, andillustration and explanation of components associated with transmissionof downlink data will be omitted.

The number of receiving RF section 201 depends on the number ofantennas. Each receiving RF section 201 receives a signal transmittedfrom a terminal (transmitting apparatus 100 shown in FIG. 4) throughantennas, transforms the received signal into a baseband signal througha radio receiving process (downconvert, Fourier transform, P/S transformand the like), and outputs the transformed baseband signal to channelestimating section 202 and spatial demultiplexing synchronizationdetecting section 203.

The number of sections for each of the sections from channel estimatingsections 202 to PDCCH generating sections 211 depends on the number ofterminals which the base station (receiving apparatus 200) cancommunicate with at the same time.

Channel estimating section 202 performs channel estimation based on areference signal (DMRS) included in the baseband signal and calculates achannel estimation value. In this process, channel estimating section202 identifies the spreading codes used in the DMRS in accordance withan instruction from scheduling section 212. Channel estimating section202 then outputs the calculated channel estimation value to PDCCHgenerating section 211 and spatial demultiplexing synchronizationdetecting section 203.

Spatial demultiplexing synchronization detecting section 203demultiplexes the baseband signals mapped to a plurality of layers,using the channel estimation value and outputs the demultiplexedbaseband signals to layer demapping section 204.

Layer demapping section 204 combines the demultiplexed baseband signalsfor each CW and outputs the combined CW to likelihood generating section206.

The number of error detecting sections 205 depends on the number of CWs.Each of error detecting section 205 includes likelihood generatingsection 206, retransmission combining section 207, decoding section 208,and CRC detecting section 209.

Likelihood generating section 206 calculates likelihood for each CW andoutputs the calculated likelihood to retransmission combining section207.

Retransmission combining section 207 stores past likelihoods for each CWand performs a retransmission-combining process on the retransmissiondata, based on the RV parameter and outputs the combining-processedlikelihood to decoding section 208.

Decoding section 208 decodes a likelihood obtained through theretransmission-combining process to generate decoded data and outputsthe generated decoded data to CRC detecting section 209.

CRC detecting section 209 performs an error detecting process by CRC onthe decoded data outputted from decoding section 208 and outputs theresult of error detection for each CW to PHICH generating section 210and scheduling section 212. CRC detecting section 209 outputs thedecoded data as received data.

PHICH generating section 210 allocates ACK/NACK information indicatingthe result of error detection received from CRC detecting section 209associated with each CW to a PHICH for each CW. The PHICH is providedwith an ACK/NACK resource as a response resource for each CW. Forexample, PHICH generating section 210 allocates an ACK to the ACK/NACKresource for the CW0 when the result of error detection for the CW0indicates the absence of an error, and allocates a NACK to the ACK/NACKresource for the CW0 when the result of error detection for the CW0indicates the presence of an error. Similarly, PHICH generating section210 allocates an ACK to an ACK/NACK resource corresponding to CW1 whenthe result of error detection with respect to CW1 indicates the absenceof an error, and allocates a NACK to the ACK/NACK resource correspondingto CW1 when the result of error detection with respect to CW1 indicatesthe presence of an error. In view of the above, PHICH generating section210, as a response signal generating section, allocates an ACK or a NACKto a response resource provided in the PHICH for each CW. In this way,the ACK/NACK information indicating the result of error detection foreach CW is allocated to the PHICH and transmitted to the terminal(transmitting apparatus 100) (not shown).

PDCCH generating section 211 estimates the channel condition based onthe channel estimation value calculated by channel estimating section202. Then, PDCCH generating section 211 determines transmissionparameters for a plurality of terminals based on the estimated channelcondition. In this process, PDCCH generating section 211 sets aspreading code resource used for the DMRS allocated to each terminal inaccordance with an instruction from scheduling section 212. PDCCHgenerating section 211 allocates the set transmission parameters to thePDCCH. In this way, the transmission parameters for each terminal areallocated to the PDCCH and transmitted to each terminal (not shown).

Scheduling section 212 allocates any of a plurality of spreading coderesources to the DMRS transmitted from each terminal and generated foreach layer to which the CW transmitted by the terminal is allocated,based on the result of error detection inputted from CRC detectingsection 209 associated with each CW. Then, scheduling section 212indicates the spreading code resource allocated to each terminal toPDCCH generating section 211 associated with that terminal. Furthermore,scheduling section 212 indicates the spreading code resource allocatedto each terminal to channel estimating section 202 associated with thatterminal.

The operations of transmitting apparatus 100 (hereinafter, referred toas “a terminal”) and receiving apparatus 200 (hereinafter, referred toas “a base station”) configured as described above will now bedescribed.

The terminal transmits a reference signal (SRS: Sounding ReferenceSignal) for estimating a channel condition (for measuring channelquality) in accordance with an instruction from the base station.

The base station receives the reference signal (SRS) and, based on theresult of observation of the received signal, determines transmissionparameters including allocated frequency resources (allocated RBs), atransmission rank number, a precoder, a modulation scheme, a codingrate, RV parameters used in retransmission, or spreading codes used inthe reference signal (DMRS) associated with the 0-th layer (k=0, Layer0). The base station reports the determined transmission parameters tothe terminal through PDCCH. The terminal needs time corresponding toabout four subframes to generate transmission data in LTE, for example.Thus, the base station needs to report resource allocation in the(n−4)-th subframe in order to generate transmission data transmitted inthe n-th subframe. Therefore, the base station determines and reportstransmission parameters based on a channel condition in the (n−4)-thsubframe.

Then, the terminal extracts the transmission parameters from the PDCCH,generates the DMRS and a data signal for each layer based on theextracted transmission parameters, and performs a precoding on the DMRSand the data signal, thereby forming a transmission signal to betransmitted from each transmission antenna. The terminal transmits thegenerated transmission signal to the base station.

The spreading codes used in the DMRS associated with each layer (k=1, 2or 3, Layer 1, 2 or 3) is determined based on the value for that layerrelative to the value for the 0-th layer (k 0, Layer 0) which isincluded in the transmission parameters, as described above. In otherwords, the spreading codes for each of Layers 1, 2 and 3 is determinedbased on the spreading codes for Layer 0 (the spreading code included inthe transmission parameters). The terminal also retains the spreadingcodes of the DMRS indicated through the PDCCH.

The base station performs a receiving process on the transmission signaltransmitted from the terminal in the n-th subframe and generates thePHICH based on the result of error detection for each CW. In LTE, thebase station can issue a retransmission instruction through the PDCCH aswell as through the PHICH. However, such a situation is not closelyrelated to the present invention and thus will not be described indetail.

The terminal refers to the PDCCH and the PHICH at a timing when theresult of error detection is reported from the base station (in thiscase, the (n+4)-th subframe in LTE). The PHICH includes an instructionfor HARQ.

When detecting an ACK from the PHICH, the terminal determines that thebase station could successfully demodulate the corresponding CW andstops retransmission of the CW. On the other hand, when not detecting anACK in the PHICH, the terminal determines that the base station couldnot demodulate the corresponding CW and instructs the CW to beretransmitted, and retransmits the CW at predetermined timing.

According to the aforementioned example, when not detecting an ACKcorresponding to a CW transmitted in the n-th subframe, the terminaltransmits retransmission data of the CW in the n+8-th subframe. For thistransmission, as described above, the terminal uses the sametransmission parameters (precoder, for example) as those indicatedthrough the PDCCH in the (n−4)-th subframe, except that a predeterminedvalue depending on the number of retransmission requests is used as theRV parameter, and values (spreading code resources) set in accordancewith values (spreading code resources) stored in retransmissionspreading code storage section 111 and the occurrences of ACKs and NACKsare used for the spreading codes of the DMRSs. A method of setting thespreading codes used in the DMRS in retransmission will be describedhereinafter.

When the result of error detection of a CW indicates the absence of anerror, the base station reports an ACK to the terminal, through a PHICHand instructs the transmission of the corresponding CW to be stopped.When the result of error detection of a CW indicates the presence of anerror, the base station reports a NACK to the terminal through thePHICH. The base station performs a retransmission combining process andrepeats a demodulating process. The base station performs demodulationof the retransmission data and resource allocation to another terminalbased on the spreading code resources set in accordance with thespreading code resources indicated to the terminal in the firsttransmission and the result of error detection of the CW.

Next, a method of setting the spreading codes used in the DMRS inretransmission will be described.

In the following, as shown in FIG. 6, a case where the firsttransmission is transmission using three layers, as in the case shown inFIG. 3, will be described. That is, in the first transmission, CW0 istransmitted in the 0-th layer (k=0, Layer 0), CW1 is transmitted in twolayers of the first layer (k=1, Layer 1) and the second layer (k=2,Layer 2). The spreading codes used for Layers 0 to 2 in the firsttransmission are n_(CS,0)=0 and n_(OCC,0)=0, n_(CS,1)=6 and n_(OCC,1)=0,and n_(CS,2)=3 and n_(OCC,2)=1, respectively. As shown in FIG. 6, it isassumed that only CW1 is retransmitted (reTX) as a result of errordetection at the base station (that is, CW0: ACK, and CW1: NACK).

In retransmission of CW1 shown in FIG. 6, if the terminal uses the samespreading code resource for the DMRS (that is, set values stored inretransmission spreading code storage section 111) as that used in thefirst transmission, different OCCs (n_(OCC,2)=0 and 1) are applied tothe two layers, Layers 1 and 2, to which CW1 is allocated, as in thecase shown in FIG. 3.

Thus, when DMRS generating section 110 receives a response signalrequesting for retransmission of only a single CW allocated to aplurality of layers, DMRS generating section 110 uses, for the DMRSgenerated for the plurality of layers, spreading code resources havingthe same OCC from among the plurality of spreading code resourcesdefined by the plurality of OCCs (n_(OCC,k)=0, 1, in this example). Thatis, in a situation where different OCCs are applied to a plurality oflayers to which the CW to be retransmitted is allocated when thespreading code resources for the DMRSs used in the first transmissionare used in the retransmission, the terminal adjusts the spreading coderesources for the DMRSs so that the spreading code resources having thesame OCC for the plurality of layers to which the CW to be retransmittedis allocated are applied to the DMRSs.

To be more specific, the terminal uses spreading code resources havingthe same OCC from among the spreading code resources used for the DMRSsgenerated for a plurality of layers in the first transmission (that is,set values stored in retransmission spreading code storage section 111),for the DMRSs generated for the plurality of layers to which the CW tobe retransmitted is allocated. For example, in FIG. 6, the terminal usestwo spreading codes having the same OCC (n_(OCC,k)=0) in retransmission,from among the three spreading code resources used in the firsttransmission. As shown in FIG. 6, two spreading codes n_(CS,1)=0 andn_(OCC,1)=0, and n_(CS,2)=6 and n_(OCC,2)=0 are used for Layers 1 and 2,respectively, to which CW1 to be retransmitted is allocated, and thesespreading codes occupy only one OCC (n_(OCC,k)=0).

As a result, as spreading code resources that are other than thoseoccupied by Layers 1 and 2 to which CW1 to be retransmitted is allocatedand that do not interfere with the spreading code resources used forCW1, the spreading code resources in the region enclosed by the dashedline in FIG. 6 (the spreading code resources having an OCC of 1(n_(OCC,k)=1) and any cyclic shift sequence (n_(CS,k)=0 to 11)) areavailable.

On the other hand, in a situation where different OCCs are applied to aplurality of layers to which the CW to be retransmitted is allocatedwhen the spreading code resources for the DMRSs allocated to theterminal in the first transmission are used in the retransmission, thebase station recognizes that the CW (DMRS) is to be retransmitted usingthe spreading code resources having the same OCC from among thespreading code resources for the DMRSs allocated to the terminal in thefirst transmission. And the base station demodulates the retransmittedCW using the spreading codes having the same OCC described above fromamong the spreading code resources for the DMRS allocated to theterminal in the first transmission. Furthermore, the base stationperforms resource allocation to another terminal (a new user) takinginto consideration that, from among the spreading code resources for theDMRS allocated in the first transmission, the spreading codes having thesame OCC are used for the CW retransmitted.

That is, when only the result of error detection of a single CWallocated to a plurality of layers shows a NACK, the base stationidentifies the spreading code resources used for the DMRS for theplurality of layers transmitted by the terminal that retransmits thesingle code word as spreading code resources having the same OCC fromamong the plurality of spreading code resources. Furthermore, the basestation allocates, from among the plurality of spreading code resources,spreading code resources having different OCCs than the OCC used by theterminal that performs the retransmission (the identified OCC) to theDMRSs transmitted by another terminal apparatus (a new user) differentfrom the terminal that performs the retransmission.

For example, in FIG. 6, the result of error detection of the datareceived from CRC detecting section 209 is “CW0: absence of an error andCW1: presence of an error”. Therefore, scheduling section 212 identifiesthat CW1 to be retransmitted next time from the terminal is generatedusing the DMRSs for the spreading code resources different from those inthe first transmission (n_(OCC,1)=0, n_(OCC,2)=1 shown in FIG. 6) andhaving the same OCC (n_(OCC,1)=0, n_(OCC,2)=0 shown in FIG. 6). Then,scheduling section 212 indicates to channel estimating section 202 thatthe two spreading code resources, n_(CS,1)=0 and n_(OCC,1)=0, andn_(CS,2)=6 and n_(OCC,2)=0, are the spreading code resources applied toCW1 to be retransmitted.

Furthermore, as resources to be allocated to the DMRSs for anotherterminal (a new user) different from the terminal that retransmits CW1shown in FIG. 6, scheduling section 212 uses spreading code resourcesthat are other than the spreading code resources used for CW1 to beretransmitted (n_(OCC,1)=0 shown in FIG. 6) and do not interfere withthe spreading code resources used for CW1. In other words, schedulingsection 212 can allocate the spreading code resources in the regionenclosed by the dashed line in FIG. 6, where the spreading coderesources have an OCC of 1 (n_(OCC,k)=1) and any cyclic shift sequences(n_(CS,k)=0 to 11), to the DMRSs for another terminal.

Therefore, for example, even in the case where a scheduler is tomultiplex a new user that performs transmission using two layers as amultiuser MIMO operation (that is, in the case where spreading codeshaving the same value of OCC and values of n_(CS,k) that differ by 6 orso are used), spreading code resources whose values of n_(CS,k) differby 6 or so in the region enclosed by the dashed line in FIG. 6 can beallocated. In, this, way, as shown in FIG. 6, the DMRS for theretransmission data (CW1) and DMRSs for another terminal can bemultiplexed.

As described above, on the side of the terminal (transmitting apparatus100), in the case where a response signal that requests forretransmission of only a single code word allocated to a plurality oflayers is received, DMRS generating section 110 uses spreading coderesources having the same OCC from among a plurality of spreading coderesources, for the DMRSs generated for the plurality of layers to whichthe code word to be retransmitted is allocated. As a result, a shortageof spreading code resources in retransmission can be prevented. In otherwords, even in the case where non-adaptive HARQ control is applied usingthe PHICH, it is possible to avoid restrictions on allocation ofresources to a new user by the scheduler that would otherwise be imposeddue to the continuation of use, for retransmission, of the spreadingcode resources for different OCCs set for DMRSs for a plurality oflayers in the first transmission.

On the side of the base station (receiving apparatus 200), in the casewhere only the result of error detection of a single code word allocatedto a plurality of layers shows a NACK, scheduling section 212 identifiesthat the spreading code resources used for the DMRSs for a plurality oflayers transmitted by the terminal that retransmits the single code wordare spreading code resources having the same OCC from among a pluralityof spreading code resources. Furthermore, from among a plurality ofspreading code resources, scheduling section 212 allocates, to DMRSstransmitted by another terminal (a new user) different from the terminalthat performs the retransmission, spreading code resources havingdifferent OCCs than the OCC used by the terminal that performs theretransmission (the same OCC for the layers). Accordingly, resources areadequately allocated to each terminal in application of multiuser MIMO.

Therefore, according to the present embodiment, the scheduler canperform spreading code allocation by avoiding restrictions on allocationof resources to a new user even in the case where non-adaptive HARQcontrol is applied using the PHICH.

Embodiment 2

According to Embodiment 2, spreading code resources for the same OCC areused for DMRS generated for a plurality of layers to which one CW to beretransmitted is allocated, as in Embodiment 1. However, the presentembodiment differs from Embodiment 1 in that the OCC used by theterminal (the same OCC for the layers) is changed each timeretransmission occurs.

In the following, the present embodiment will be described in detail.

FIG. 7 is a block diagram showing a configuration of main components ofa transmitting apparatus according to the present embodiment. Intransmitting apparatus 300 according to the present embodiment in FIG.7, components in FIG. 7 common to FIG. 4 are assigned the same referencenumerals as in FIG. 4, and descriptions thereof are omitted here.Transmitting apparatus 300 shown in FIG. 7 is transmitting apparatus 100shown in FIG. 4 in which retransmission number counting section 301 isadditionally provided, and retransmission spreading code storage section111 is replaced with retransmission spreading code storage section 302.

For each CW received from ACK/NACK demodulating section 102, if theACK/NACK information shows a NACK, retransmission number countingsection 301 increments the number of retransmissions for the CW andstores the number in the interior. In other words, retransmission numbercounting section 301 counts the number of retransmissions for each CWand stores the counted number of retransmissions for each CW. Inaddition, for each CW, if the ACK/HACK information shows an ACK,retransmission number counting section 301 resets the number ofretransmissions for the CW. Then, retransmission number counting section301 outputs the counted number of retransmissions for each CW toretransmission spreading code storage section 302.

Retransmission spreading code storage section 302 sets the OCC inaccordance with the number of retransmissions received fromretransmission number counting section 301 in accordance with apredetermined rule concerning the OCCs included in the spreading coderesources. For example, in an odd-numbered retransmission,retransmission spreading code storage section 302 outputs the storedspreading code resources without change to DMRS generating section 110,as in Embodiment 1. On the other hand, in an even-numberedretransmission, retransmission spreading code storage section 302outputs the stored spreading code resources with their OCCs inverted toDMRS generating section 110. Note that the operations of retransmissionspreading code storage section 302 are not limited to the processesdescribed above, and the operation in the odd-numbered retransmissionand the operation in the even-numbered retransmission may beinterchanged.

As in Embodiment 1, in retransmission of only a single CW allocated to aplurality of layers, DMRS generating section 110 uses spreading coderesources having the same OCC for the DMRSs generated for the pluralityof layers to which the CW to be retransmitted is allocated. However, foreach retransmission, DMRS generating section 110 changes the OCC usedfor the DMRSs generated for the plurality of layers to which the singleCW to be retransmitted is allocated (the same OCC for the layers).

For example, as shown in FIG. 6, it is assumed that the firsttransmission is transmission using three layers, and the spreading codesused for the layers (k=0, 1 and 2, Layers 0, 1 and 2) are n_(CS,0)=0 andn_(OCC,0)=0, n_(CS,1)=6 and n_(OCC,1)=0, and n_(CS,2)=3 and n_(OCC,2)=1.

Here, as shown in FIG. 6, it is assumed that only CW1 allocated toLayers 1 and 2 (k=1,2) is to be retransmitted. In this case, in theodd-numbered (first, third, fifth and so on) retransmissions, DMRSgenerating section 110 uses the two spreading codes (n_(CS,1)=0 andn_(OCC,1)=0, and n_(CS,2)=6 and n_(OCC,2)=0) having the same OCC(n_(OCC,k)=0) without change, as shown in FIG. 6.

On the other hand, in the even-numbered (second, fourth, sixth and soon) retransmissions, DMRS generating section 110 uses the spreading coderesources (n_(CS,1)=0 and n_(OCC,1)=1, and n_(CS,2)=6 and n_(OCC,2)=1)obtained by inverting the OCC of the two spreading codes for the sameOCC (n_(OCC,k)=0) (n_(CS,1)=0 and n_(OCC,1)=0, and n_(CS,2)=6 andn_(OCC,2)=0) (that is, the OCC is inverted from n_(OCC,k)=0 ton_(OCC,k)=1) (not shown).

As a result, the DMRSs generated for the plurality of layers to whichthe CW to be retransmitted is allocated occupy spreading code resourceshaving different OCCs in each retransmission. For example, in FIG. 6, ineach of Layers 1 and 2 (k=1, 2) to which CW1 to be retransmitted isallocated, spreading code resources having one OCC (n_(OCC,k)=0) areoccupied in the odd-numbered retransmissions, and spreading coderesources having the other OCC (n_(OCC,k)=1) are occupied in theeven-numbered retransmissions.

On the other hand, on the side of the base station (receiving apparatus200 (FIG. 5)), scheduling section 212 has the same function (not shown)as that of retransmission number counting section 301 of the terminaland outputs spreading code resources having different OCCs changed inaccordance with the counted number of retransmissions of each CW tochannel estimating section 202 in the same manner as the terminal(transmitting apparatus 300). Furthermore, as in Embodiment 1, fromamong a plurality of spreading code resources, scheduling section 212allocates spreading code resources having different OCCs than the OCCused by the terminal that performs the retransmission (the same OCC fora plurality of layers) to the DMRSs transmitted by another terminal (anew user) different from the terminal instructed to retransmit the CWallocated to the plurality of layers.

With such a configuration, according to the present embodiment, it ispossible to avoid using a particular OCC (either one of n_(OCC,k)=0 or1, for example) on the terminal that retransmits only the CW allocatedto a plurality of layers. Therefore, the present embodiment not onlyachieves the same advantages as those of Embodiment 1 but also allowsmultiplexing of another terminal using different spreading codes foreach retransmission of the CW.

Embodiment 3

In Embodiments 1 and 2, cases have been described in which spreadingcode resources used for DMRSs used in CW retransmission are adjusted inaccordance with the spreading code resources used in the firsttransmission and the occurrences of ACKs and NACKs. According to thepresent embodiment, spreading code resources used for DMRSs used in CWtransmissions (the first transmission and the subsequentretransmissions) are adjusted in accordance with the spreading coderesources and the number of transmission layers (the transmission ranknumber) reported through the PDCCH.

In the following, the present embodiment will be described in detail.

FIG. 8 is a block diagram showing a configuration of main components ofa transmitting apparatus according to the present embodiment. Intransmitting apparatus 400 according to the present embodiment in FIG.8, components in FIG. 8 common to FIG. 4 are assigned the same referencenumerals as in FIG. 4, and descriptions thereof are omitted here.Transmitting apparatus 400 shown in FIG. 8 is transmitting apparatus 100shown in FIG. 4 in which retransmission spreading code storage section111 is replaced with spreading code adjusting section 401.

In transmitting apparatus 400 (terminal) shown in FIG. 8, DMRSgenerating section 110 calculates, based on the spreading codes(n_(CS,0) and n_(OCC,0), for example) used for the DMRS associated withthe 0-th layer (k=0, Layer 0) included in the transmission parametersreported from the base station through the PDCCH, spreading codes usedfor the DMRS associated with each of the other layers (k=1, 2 and 3,Layers 1, 2 and 3), as in Embodiment 1. Then, DMRS generating section110 outputs the calculated spreading codes (the spreading codes used foreach of the layers (k=0 to 3)) and the transmission rank number (thatis, the number of transmission layers) included in the transmissionparameters to spreading code adjusting section 401.

Spreading code adjusting section 401 adjusts the spreading codesreceived from DMRS generating section 110 based on the transmission ranknumber received from DMRS generating section 110. To be more specific,spreading code adjusting section 401 adjusts (resets) the spreadingcodes used for the respective number of transmission layers so thatspreading code resources having the same OCC are allocated to the DMRSsgenerated for each of the plurality of layers to which the same CW isallocated, by referring to the relationship between the layersdetermined by the value of the transmission rank number (the number oftransmission layers) and the CWs.

Then, DMRS generating section 110 generates DMRSs using the spreadingcodes (adjusted spreading codes) received from spreading code adjustingsection 401 and outputs the generated DMRSs to precoding section 109. Ifthe ACK/NACK information received from ACK/NACK demodulating section 102shows a NACK (that is, if a retransmission is required), DMRS generatingsection 110 uses the same spreading codes used in the first transmission(adjusted spreading codes) without change.

Next, a spreading code adjusting process performed by spreading codeadjusting section 401 will be described in detail.

Spreading code adjusting section 401 receives spreading code resourcesused for the DMRS for each layer (Layer 0 to 3), from DMRS generatingsection 110. To be more specific, as shown in the left half of FIG. 9,the spreading codes for Layer 0 (k=0) are n_(CS,0)=0 and n_(OCC,0)=0,the spreading codes for Layer 1 (k=1) are n_(CS,1)=6 and n_(OCC,1)=0,the spreading codes for Layer 2 (k=2) are n_(CS,2)=3 and n_(OCC,2)=1,and the spreading codes for Layer 3 (k=3) are n_(CS,3)=9 andn_(OCC,3)=1.

As described above, in transmission using three layers, as therelationship between the layers and the CWs, CW0 is allocated to Layer 0(k=0), and CW1 is allocated to Layers 1 and 2 (k=1, 2). Accordingly, asshown in the left half of FIG. 9, if the terminal uses the spreadingcode resources for the DMRSs indicated through the PDCCH (that is, theset values inputted to spreading code adjusting section 401) withoutchange, different OCCs (n_(OCC,2)=0, 1) are applied to the two layers,Layers 1 and 2, to which CW1 is allocated, as in the case shown in FIG.3. In other words, different OCCs are used in the DMRSs generated forthe plurality of layers to which the same CW is allocated.

In view of this, spreading code adjusting section 401 adjusts thespreading code resource used in each layer for the respective number oftransmission layers so that spreading code resources for the same OCCare used for the DMRSs generated for the plurality of layers to whichthe same CW is allocated.

To be more specific, as shown in the right half of FIG. 9, spreadingcode adjusting section 401 adjusts spreading code resources n_(CS,0)=0and n_(OCC,0)=0 for k=0, n_(CS,2)=3 and n_(OCC,2)=1 for k=2, andn_(CS,3)=9 and n_(OCC,3)=1 for k=3 as the spreading code resources usedin transmission using three layers (three layers shown in FIG. 9). Inother words, spreading code adjusting section 401 uses the spreadingcodes n_(CS,3)=9 and n_(OCC,3)=1 for =3 used in transmission using fourlayers, instead of the spreading codes n_(CS,1)=6 and n_(OCC,1)=0 fork=1 that would otherwise be used in transmission using three layers.

As a result, as shown in the left half of FIG. 10, in the firsttransmission using three layers, DMRS generating section 110 generates aDMRS using n_(CS,0)=0 and n_(OCC,0)=0 for Layer 0 (k=0) to which CW0 isallocated, and generates a DMRS using n_(CS,1)=3 and n_(OCC,1)=1, andn_(CS,2)=9 and n_(OCC,2)=1 for Layers 1 and 2 to which CW1 is allocated,respectively.

In other words, spreading code resources for the same OCC (n_(OCC,k)=1)are used for the DMRSs generated for the two layers, Layers 1 and 2, towhich CW1 is allocated.

In the case where the terminal (transmitting apparatus 400) detects noACK for a CW transmitted therefrom, the terminal is to transmitretransmission data for the CW. In the retransmission, DMRS generatingsection 110 uses the spread code resources used for the DMRSs in thefirst transmission (that is, the adjusted spreading code resources shownin the right half of FIG. 9) without change. For example, in FIG. 10, inthe case where retransmission of only CW1 occurs, DMRS generatingsection 110 uses the spreading code resources (n_(CS,1)=3 andn_(OCC,1)=1, and n_(CS,2)=9 and n_(OCC,2)=1) used in the firsttransmission for the DMRSs generated for the two layers, Layers 1 and 2,to which CW1 is allocated.

As a result, as shown in the right half of FIG. 10, even when only CW1allocated to a plurality of layers is to be retransmitted, the spreadingcode resources having an OCC of 0 (n_(OCC,k)=0) and any cyclic shiftsequence (n_(CS,k)=0 to 11), that is, the spreading code resources inthe region enclosed by the dashed line, are available as spreading coderesources that can be allocated to another terminal (a new user) thatcan be multiplexed in the same resource.

On the other hand, on the side of the base station (receiving apparatus200 (FIG. 5)), scheduling section 212 has the same function (not shown)as that of spreading code adjusting section 401 of the terminal andoutputs the adjusted (reset) spreading code resources to channelestimating section 202 in the same manner as the terminal (transmittingapparatus 400). Furthermore, from among a plurality of spreading coderesources, scheduling section 212 allocates, to the DMRSs transmitted byanother terminal (a new user) different from the terminal instructed toretransmit only the CW allocated to the plurality of layers, spreadingcode resources having different OCCs than the OCC used by the terminalthat performs the retransmission (the same OCC for a plurality oflayers). As a result, an appropriate resource is allocated to eachterminal even in the case where the multiuser MIMO is applied.

Therefore, for example, in FIG. 10, even in the case where the scheduleris to multiplex an LTE terminal (a new user) that is only capable of anmultiuser MIMO operation using an OCC of 0 (n_(OCC,k)=0), a sufficientamount of resources can be provided for the LTE terminal.

As described above, according to the present embodiment, in preparationfor occurrence of retransmission, the terminal (transmitting apparatus400) uses, in the first transmission, spreading code resources havingthe same OCC from among a plurality of spreading codes for DMRSsgenerated for a plurality of layers to which the same CW, which is aunit of retransmission, is allocated. As a result, a shortage ofspreading code resources in retransmission can be prevented. In otherwords, even in the case where non-adaptive HARQ control is applied usingthe PHICH (even in the case where the spreading codes for the DMRScannot be reported through the PHICH), it is possible to avoidrestrictions on allocation of resources to a new user by the schedulerthat would otherwise be imposed due to the use, for retransmission, ofspreading code resources for different OCCs.

Therefore, according to the present embodiment, as in Embodiment 1, thescheduler can perform spreading code allocation by avoiding restrictionson allocation of resources to a new user even in the case wherenon-adaptive HARQ control is applied using the PHICH.

Embodiments of the present invention have been described above.

Although the present invention has been described above with embodimentsusing antennas, the present invention is equally applicable to antennaports.

An antenna port refers to a theoretical antenna comprised of one or aplurality of physical antennas. In other words, “antenna port” does notnecessarily refer to one physical antenna, but may refer to an arrayantenna and so forth composed of a plurality of antennas.

For example, 3 GPP LTE does not define how many physical antennas anantenna port is formed with, but defines that an antenna port is theminimum unit for transmitting different reference signals in a basestation.

In addition, an antenna port may be defined as a minimum unit formultiplying a precoding vector as weighting.

Although an example of the present invention configured as hardware hasbeen described in the present embodiments, the present invention mayalso implement software in collaboration with hardware.

Furthermore, each function block employed in the above descriptions ofembodiments may typically be implemented as an LSI constituted by anintegrated circuit. These may be implemented individually as singlechips, or a single chip may incorporate some or all of the functionblocks. “LSI” is adopted here but this may also be referred to as “IC,”“system LSI,” “super LSI,” or “ultra LSI” depending on differing extentsof integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI production, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be reconfigured may also bepossible.

In the event of the introduction of a circuit implementation technologywhereby LSI is replaced by a different technology, which is advanced inor derived from semiconductor technology, integration of the functionblocks may of course be performed using technology therefrom. Anapplication to biotechnology and/or the like is also possible.

The disclosure of Japanese patent application No. 2010-181344, filed onAug. 13, 2010, including the specifications, drawings and abstracts, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

A terminal apparatus, a base station apparatus, a retransmission method,and a resource allocation method according to the present invention aresuitable for performing a method of controlling retransmission usingnon-adaptive HARQ in a radio communication system using a MIMOcommunication technique.

REFERENCE SIGNS LIST

-   100, 300, 400 Transmitting apparatus-   101 PDCCH demodulating section-   102 ACK/NACK demodulating section-   103 Code word generating section-   104 Coding section-   105 Rate matching section-   106 Interleaving/scrambling section-   107 Modulating section-   108 Layer mapping section-   109 Precoding section-   110 DMRS generating section-   111, 302 Retransmission spreading code storage section-   112 SRS generating section-   113 SC-FDMA signal generating section-   200 Receiving apparatus-   201 Receiving RF section-   202 Channel estimating section-   203 Spatial demultiplexing synchronization detecting section-   204 Layer demapping section-   205 Error detecting section-   206 Likelihood generating section-   207 Retransmission combining section-   208 Decoding section-   209 CRC detecting section-   210 PHICH generating section-   211 PDCCH generating section-   212 Scheduling section-   301 Retransmission number counting section-   401 Spreading code adjusting section

1. A terminal apparatus comprising: a code word generating section thatgenerates a code word by encoding a data sequence; a mapping sectionthat allocates each code word to one or a plurality of layers; areference signal generating section that generates a reference signalfor each of the layers to which the code word is allocated, using any ofresources from among a plurality of resources defined by a plurality ofcodes orthogonal to each other; and a receiving section that receives aresponse signal indicating a retransmission request for the code word,wherein in a case where the received response signal is to request forretransmission of only a single code word allocated to the plurality oflayers, the reference signal generating section uses resources having asame code from among the plurality of resources, for the referencesignal generated for each of the plurality of layers.
 2. The terminalapparatus according to claim 1, further comprising: a storage sectionthat stores the resources used for the reference signal generated foreach of the plurality of layers in a first transmission, wherein thereference signal generating section uses resources having a same codefrom among the resources stored in the storage section, for thereference signal generated for each of the plurality of layers in aretransmission.
 3. The terminal apparatus according to claim 1, whereinthe reference signal generating section changes, for eachretransmission, the same code used for the reference signal generatedfor each of the plurality of layers.
 4. A base station apparatuscomprising: a receiving section that receives a code word allocated toone or a plurality of layers; a detecting section that detects an errorof the received code word; a response signal generating section thatgenerates a response signal indicating a result of error detection ofthe code word; and a scheduling section that allocates any of resourcesfrom among a plurality of resources defined by a plurality of codesorthogonal to each other, to the reference signal to be transmitted fromeach terminal apparatus and to be generated for each of the layers towhich the code word is allocated, wherein in a case where only theresult of error detection of a single code word allocated to theplurality of layers shows a NACK, the scheduling section identifiesresources used for the reference signal for each of the plurality oflayers transmitted from a terminal apparatus to retransmit the singlecode word, as resources having a same code from among the plurality ofresources, and allocates a resource having a different code than thesame code from among the plurality of resources, to the reference signaltransmitted from another terminal apparatus different from the terminalapparatus to perform the retransmission.
 5. A retransmitting methodcomprising: generating a code word by encoding a data sequence;allocating each code word to one or a plurality of layers; generating areference signal for each of the layers to which the code word isallocated, using any of resources from among a plurality of resourcesdefined by a plurality of codes orthogonal to each other; and receivinga response signal indicating a retransmission request for the code word,wherein in a case where the received response signal is to request forretransmission of only a single code word allocated to the plurality oflayers, resources having a same code from among the plurality ofresources are used for the reference signal generated for each of theplurality of layers.
 6. A resource allocating method comprising:receiving a code word allocated to one or a plurality of layers;detecting an error of the received code word; generating a responsesignal indicating a result of error detection of the code word; andallocating any of resources from among a plurality of resources definedby a plurality of codes orthogonal to each other, to the referencesignal to be transmitted from each terminal apparatus and to begenerated for each of the layers to which the code word is allocated,wherein in a case where only the result of error detection of a singlecode word allocated to the plurality of layers shows a NACK, resourcesused for the reference signal for each of the plurality of layerstransmitted from a terminal apparatus to retransmit the single code wordare identified as resources having a same code from among the pluralityof resources, and a resource having a different code than the same codefrom among the plurality of resources is allocated to the referencesignal transmitted from another terminal apparatus different from theterminal apparatus to perform the retransmission.